1. Field of the Invention
The field of the invention is that of aeronautical propulsion and more particularly turbojet engines with high dilution rates, or turbofans.
2. Description of the Related Art
Modern turbomachines are conventionally produced in the form of an assembly of modules which can include fixed parts and moving parts. A module is defined as a subassembly of a turbomachine which exhibits geometrical characteristics at its interfaces with the adjacent modules that are sufficiently precise for it to be able to be shipped individually and which has undergone a particular balancing when it includes rotating parts. The modules are assembled to form a complete engine, minimizing the operations of balancing and of the matching interfaced parts.
The current turbofans comprise a number of compressor stages, notably a low-pressure (BP) and a high-pressure (HP) compressor which belong to the primary core of the engine. Upstream of the low-pressure compressor, there is a wheel of large moving blades or fan, which feeds both the primary flow which passes through the BP and HP compressors and the cold flow, or secondary flow, which is directed to a cold flow nozzle, called secondary nozzle. The fan is driven by the rotation shaft of the BP core and generally rotates at the same speed. It may, however, be advantageous to have the fan rotate at a rotation speed less than that of the BP shaft, particularly when the latter is of very large size, in order to better adapt it aerodynamically. For this, a reduction gear is positioned between the BP shaft and a fan shaft, which bears the fan. The fan, the fan shaft and the reduction gear generally form part of one and the same module, called fan module.
One of the problems encountered with the reduction gears on turbofans is that they require high oil flow rates, which can be as high as 6 to 7000 l/h on take-off, to ensure their lubrication and the cooling of their pinions and main bearings. To limit the losses by churning, it is necessary to bring the oil precisely to the required places, then evacuate it as soon as its lubrication action has been performed.
Among the types of reduction gears used, there are reduction gears with epicycloidal gear trains, which have the advantage of offering high rotation speed reduction rates, in small footprints. On the other hand, they have the drawback of having planet pinions which move by rotating about the axis of rotation of the reduction gear drive shaft. It is therefore essential to devise devices for supplying the oil, which comes from an oil tank and a lubrication pump situated at fixed coordinates, to these pinions which are situated at moving coordinates. To resolve this problem, the devices commonly used comprise systems of rotating seals, produced from segments which rotate while rubbing against the fixed parts and which ensure the seal-tightness between the fixed parts and the moving parts of the reduction gear.
These systems nevertheless have the drawbacks of a consequential footprint and a wear which is incompatible with the lifetimes demanded of aeronautical engines. They also exhibit risks of failures which would give rise to an interruption of the oil feed, which is not acceptable given the potentially catastrophic consequences of an engine stopping in flight as a result of a jamming of its reduction gear. Finally, it is difficult to make these reduction gears compatible with a flexible installation on the structure of the engine, which is recommended to mitigate the risk of loss or rupture of a fan blade, or even with an installation of modular type to facilitate the assembly of an engine.